<!doctype html>
<meta charset="utf-8">
<title>CSS Test Reference</title>
<style>
  .container {
    width: 500px;
  }
  .kid {
    height: 50px;
    background: green;
    width: 40px;
  }
</style>
<div class="container">
  <div class="kid"></div>
</div>
